Combating unwanted vegetation with 2-aryl-5-substituted 1,3,4-oxadiazoles

ABSTRACT

Unwanted vegetation is combated by application of a class of phenyloxadiazoles which possess either or both pre and postemergent phytotoxicity. The herbicides as a class are severely toxic to a minority of plant species, most of the compounds having pre-emergent effectiveness against crabgrass. Some of the compounds, as for example, 2-(3&#39;&#39;,4&#39;&#39;-dichlorophenyl)-5-methyl1,3,4-oxadiazole, are particularly useful for pre-emergent control of weeds in a standing crop because of an almost total absence of post-emergent phytotoxicity. A small group of compounds, such as 2-dimethylamino-5-(2&#39;&#39;,4&#39;&#39;dimethylphenyl)-1,3,4-oxadiazole are predominantly post-emergent herbicides and a number of compounds, as for instance, 2diethylamino-5-p-tolyl-1,3,4-oxadiazole, have both pre- and postemergent activity and are useful in combating both crabgrass and broadleaf weeds in fields of small grains and in brome grass pastures.

United States Patent 1 Dahle et al.

[ 51 Feb. 27, 1973 COMBATING UNWANTED VEGETATION WITH Z-ARYL-SSUBSTITUTED 1,3,4-OXADIAZOLES [75] Inventors: Norman A. Dahle, Mission;William C. Doyle, Jr., Leawood, both of [21] Appl. No.: 869,369

[52] US. Cl. ..71/92, 260/307 G [51] Int. Cl. ..A0ln 9/22 [58] Field ofSearch ..7 1/92 [56] References Cited UNITED STATES PATENTS 3,203,9598/1965 Hoffman ..71/92 X 3,564,606 2/1971 Breuer. ..71/92 X FOREIGNPATENTS OR APPLICATIONS 1,063,799 3/1967 Great Britain ..71/92 4,520,5197/1970 Japan ..71/92 Primary Examiner-James 0. Thomas, Jr.Attorney-Richard L. Kelly, Carl A. Cline and Forrest D. Stine I [57]ABSTRACT Unwanted vegetation is combated by application of a class ofphenyloxadiazoles which possess either or both pre and post-emergentphytotoxicity. The herbicides as a class are severely toxic to aminority of plant species, most of the compounds having preemergenteffectiveness against crabgrass. Some of the compounds, as for example,2-(3',4'-dichlorophenyl)- S-methyl-l,3,4-oxadiazole, are particularlyuseful for pre-emergent control of weeds in a standing crop because ofan almost total absence of post-emergent phytotoxicity.

A small group of compounds, such as 2- dimethylamino-S-(Z',4'-dimethylphenyl)- l ,3,4-oxadiazole are predominantly post-emergentherbicides and a number of compounds, as for instance, 2-diethylamino-S-p-tolyl-l,3,4-oxadiazole, have both preand post-emergentactivity and are useful in combating both crabgrass and broadleaf weedsin fields of small grains and in brome grass pastures.

23 Claims, No Drawings COMBATING UNWANTED VEGETATION WITH 2-ARYL-5-SUBS'IITUTED 1,3,4-0XADIAZOLES DESCRIPTION OF THE INVENTIONSelective herbicides which are effective to combat only a fewparticularly troublesome species or which may be used to combat severalspecies in the presence of a particularly valuable crop are scarce andmuchdesired chemical products.

The herbicides of the present invention belong to a class of2-phenyl-l,3,4-oxadiazoles having the structural formula in which R isselected from the group consisting of hydrogen, mercapto, thiocyano,amino, lower alkylamino, di(lower alkyl)amino, methyl, cyclopropyl,ethyl and propyl; R is selected from the group consisting of hydrogen,chloro and methyl; R" is selected from the group consisting of hydrogen,chloro, nitro, bromo, iodo and methyl and R' is selected from the groupconsisting of hydrogen, methyl, chloro, bromo and fluoro substituents.These substances are generally phytotoxic to less than half of a groupof test species representing about fifteen plant families. By virtue ofthis selective behavior they are useful for combating unwantedvegetation in the presence of seeds and living plants of other species.

The preparation and use of the novel herbicides are discussed below.

SYNTHESIS OF THE HERBICIDES SCHEME A N-N mi SE Ari isoN RNCO L/ ArCNHNHzor ITH-HCI Ar 0 R RU-OEt o 0 o l] E II II Ar NHNH NHR ArCHNHNCR POChlArlOJ'NHR The individual methods shown in Scheme A are specificallyexemplified below for illustrative purposes.

Method 1 0 Ar NHNHz C8: KOH

NN O 0 g II A I Ar NHNHO S K Ar 0 S H Preparation of 2-mercapto-5 (pchlorophenyl) l ,3 ,4

-oxadiazole To a stirred solution of 20 g p-chlorobenzhydrazide and 7.6g potassium hydroxide in 200 ml percent ethanol and 30 ml H,0 is addedslowly 11.7 g carbon disulfide. The resultant slurry is refluxed until H8 evolution ceases (4-6 hrs.), and the solvent is removed under reducedpressure. The residue is poured onto 200 g of ice and 30 ml ofconcentrated HCl and the precipitated product is collected andrecrystallized from ethanol, giving 14.2 g ofZ-mercapto-S-(pchlorophenyl)-l ,3,4-oxadiazole, m.p. l768. Method2 N--NAr-L Len K01I+ CNBr Ariel-SON Preparation of 2-thiocyano-5-(p-fluoro-phenyl)- 1,3 ,4-oxadiazole To a stirred solutionof 4.1 g 2-mercapto-5-(pfluorophenyl)-l,3,4-oxadiazole and 1.2 gpotassium hydroxide in 50 ml of methanol is added 2.2 g of solidcyanogen bromide. The solution is stirred an additional half hour,diluted with water and the precipitate is filtered and washed withwater, giving 3.5 g of '2-thiocyano-S-(p-fluorophenyl)-l,3,4-oxadiazole, m.p. 9 l -6 Methodjlw V a a 7 Preparation of2-amino-5-phenyl-l ,3,4-oxadiazole Benzhydrazide (70.2 g) is added to asolution of 54.1 g of cyanogen bromide in l000 ml of methanol at a ratesuch that the temperature does not rise above 40. The solution is thenstirred one-half hour at 40, refluxed one and one half hours, filteredhot, boiled down to about 500 ml and neutralized with dilute NH OH. Theresultant precipitate is collected and recrystallized from ethanol,giving 54 g of 2-amino-5-phenyl-l,3,4- oxadiazole, m.p. 234-5. Method 4Method 7 Preparation of 2-propylamino-5-(m-chloro-phenyl)-1,3,4-oxadiazole A mixture of 16.7 g1-(m-chlorobenzoyl)-4-propylsemicarbazide and 120 ml of phosphorusoxychloride is refluxed 2 hrs. Most of the solvent is distilled atreduced pressure and the residue is poured onto ice. Neutralization withconcentrated Nl-LOH gives 11.3 g of crude solid, recrystallization ofwhich from ethylene dichloride-hexane gives 4.0 g of Z-n-propylamino-S-(m-chlorophenyl)l,3,4-oxadiazole, m.p. l22.5123.0

Method 5 0 Ar NHNIh RC(OEt) Ari J-R POCla Preparation of2-cyclopropyl-5-(m-bromo-phenyl)- l ,3 ,4-oxadiazole A mixture of 8.7 gof N-(m-bromobenzoyl)-N'- cyclopropanecarbonylhydrazine and 100 ml ofphosphorus oxychloride is heated 1% hours at 85-90. The solution isconcentrated to about 50 ml by distillation at reduced pressure and theresidue is poured onto ice, precipitating 7.1 g of2-cyclopropyl-5-(mbromophcnyl)-l ,3,4-oxadiazole, m.p. 78-80.5.

O H NN Ar NHNHz R-CO Et Preparation of1-methyl-4-(l,3,4-oxa-diazol-2-yl)- pyridinium iodide A solution of 5 gof 2-(4-pyridyl)-l,3,4-oxadiazole and 7.3 g of methyl iodide in 30 ml ofN,N-dimethyl formamide is stirred 4 hours at room temperature, thendiluted with anhydrous diethyl ether, precipitating 9.3 g ofl-methyl-4-(l,3,4-oxadiazol-2-yl)-pyridinium iodide, m.p. 208-l0.Illustration of Scheme B The aryltetrazoles employed as startingmaterials in Scheme B may be prepared by the method of W. G. Finnegan,R. A. Henry and R. L. Lofquist (J. Am. Chem. Soc., 80, 3908 (1958) andU.S. Pat. 2,977,372) which utilizes the reaction of an arylnitrile witha mixture of ammonium chloride and sodium azide in dimethylformamidecontaining a catalytic amount of lithium chloride.

Method) II E 01 c3111 QQl LC...

Preparation of 2-n-propyl-5-(3,4'-dichloro-phenyl)- l ,3 ,4-oxadiazole Asolution of 5.0 g of 5-(3,4-dichlorophenyl)- tetrazole in 50 ml ofbutyric anhydride containing 10 drops of pyridine is refluxed 18 hours.Most of the excess anhydride is distilled at reduced pressure and theresidue is crystallized from hexane, giving 3.0 g of2-npropyl-S-(3',4-dichlorophenyl)-l ,3,4-oxadiazole, m.p. -82.

The 2-dialkylamino-5-aryl-l,3,4-oxadiazoles may be prepared fromZ-dialkylcarbamyl-S-aryl tetrazoles. The required tetrazoleintermediates are prepared by reacting an aryltetrazole with adialkyl-carbamyl chloride according to the following general procedure.

Preparation of 5-aryl-2-dialkyl-carbamyl-2H- tetrazoles To a stirredsolution of the appropriate tetrazole dissolved in a minimum volume ofpyridine is added dropwise the dialkylcarbamyl chloride. Keeping thetemperature below 30 by cooling the reaction flask in an ice-bath, thereaction mixture, after standing for a substantial period of time, asfor example overnight, is cooled in the ice-bath and diluted with water.The insoluble material is collected by vacuum filtration and allowed todry in air. The crude product may be putetrazole with a dialkylcarbamylchloride is placed in a test tube (30 X 7.5 cm) equipped with a magneticstirrer and immersed in an oil bath. The temperature is slowly increaseduntil the solid has melted. If the melting point of the startingmaterial is over 100 the bath temperature is held at about .80 for 1-2hours prior to increasing the temperature to the melting point. Thetemperature of the oil bath is then slowly raised to l-l30C andmaintained until the evolution of nitrogen ceases. The tube and, itscontents are allowed to cool to room temperature and the resultingproduct is purified by distillation or recrystallization from a suitablesolvent.

Hydrochlorides and other mineral acid salts of the dialkylaminosubstituent groups on the oxadiazole products are readily prepared byconventional methods. The selectivity of phytotoxicity of the salts isvery similar to that of the parent amino-substituted compounds.

USE OF THE HERBICIDES So as to illustrate clearly selective phytotoxicproperties of the herbicides, a group of controlled greenhouseexperiments is described below.

1. Post Emergent Use An aqueous dispersion of each active compound wasprepared by combining 0.4 grarn of the compound with about 4 ml of asolvent-emulsifier mixture (three parts of a commercial polyoxyethylatedvegetable oil emulsifier, one part xylene, one part kerosene) and thenadding'water, with stirring, to a final volume of 40 ml.

The 'species of plants on which each compound was to be tested wereplanted in 4-inch pots in a greenhouse. T en to 18 days after emergenceof the plants, three pots were sprayed with an aqueous dispersion of theactive compound prepared as described above, at a rate of 5 lb. ofactive compound per acre and at a spray volume of 60 gallons per acre.Approximately 1 week after the spray application the plants wereobserved and the results rated according to the following schedule:

0 no effect 1 slight effect 2 moderate effect 3 severe effect 4 maximumeffect (all plants died) The same rating schedule was employed to judgepre-emergent results obtained according to the procedure below.

2. Pre-Emergent Use A solution of each active compound was prepared bydissolving 290 mg. of the compound to be tested in 200 ml. of acetone.Disposable paper trays about 2 inches deep and half the size of ordinarygreenhouse flats were prepared and seeded with a variety of species ofplant seeds, then sprayed with the acetone solution at the rate of 10lb. of active chemical per acre of sprayed area. One tray, which hadbeen seeded with alfalfa, brome, flax, oats, radishes and sugar beetswas held at F. day temperature; another seeded with corn, coxcomb,cotton, crabgrass, millet and soybeans was held at F. Twenty-one daysafter seeding and treatment the planted trays were examined andherbicidal effect was rated according to the above schedule.

Both post-emergent and pre-emergent results are set forth in thefollowing tables. The compounds are grouped in the tables according togeneral characteristics as preor post-emergent herbicides. Those withpredominantly pre-emergent activity are useful particularly in combatingcrabgrass. The post-emergent herbicides are useful in combating variousweeds in grain crops. The compounds with both preand postemergent.activity are useful in combating crabgrass and broadleaf weeds in smallgrains, soybeans and in brome grass pastures. The data in the tableswill aid the worker in the field of weed control in selecting herbicidesfor use in specific weed control situations. By weed is meant broadlyunwanted or undesired vegetation, which in some instances may includecrop species that are in an undesirable location.

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l claim: V l. Combating unwanted vegetation by applying to the locus ofthe vegetationan effective amount of a phenyl-l,3,4-ox adiazole havingthe structural formula I in which R is selected from the groupconsisting of 10. Combating unwanted vegetation by applying to the locusof the vegetation an effective amount of 2- diethylamino-S-p-tolyl-l ,3,4-oxadiazole.

1 1. Combating unwanted vegetation by applying preemergently to thelocus of the vegetation an effective amount of 2-(m-tolyl)-5-methyl-l,3,4-oxadiazole.

l2. Combating unwanted vegetation by applying to '7 the locus of thevegetation an effective amount of 2- hydrogen, mercapto, diethylamino,dimethylamino,

2. Combating unwanted vegetation by applying preemergently to the locusof the vegetation -an effective amount of 2-( 3'-chlorophenyl)-l ,3,4-oxadiazole.

3. Combating unwanted vegetation by applying preemergently to the locusof the vegetation an effective amount of 2-( 3 '-bromophenyl )-l ,3,4-oxadiazole.

. 4. Combating unwanted vegetation by applying preemergently to thelocus of the vegetation an effective amount of2-(3'-chlorophenyl)-5-methyl-1,3,4-oxadiazole.

5. Combating unwanted vegetation by applying preemergently to the locusof the vegetation an effective amount of2-(3'-chlorophenyl)-5-propyl-l,3,4oxadiazole.

6. Combating unwanted vegetation by applying preemergently to the locusof the vegetation an efi'ective amount of2-(3'-bromophenyl)-5-methyl-1,3,4-oxadiazole.

7. Combating unwanted vegetation by applying preemergently to the locusof the vegetation an effective amount of 2-( 3 ,4'-dichlorophenyl)-5-methyl- 1 ,3 ,4-oxadiazole. *smsmsassg crabgfass'sy" a s' lyiie-aageaay to the locus of crabgrass seed an effective amount of 2- (3 ,4'-dichlorophenyl)-5 -ethyl-1 ,3 ,4-oxadiazole.

9. Combating unwanted vegetation by applying preemergently to the locusof the vegetation an effective amount of2-(3'4'-dichlorophenyl)-5-propyl-1,3,4-oxadiazole.

diethylamino-5-(4'-fluorophenyl)-1,3,4-oxadiazole.

l3. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2- dim'ethylamino-S -o-tolyl-l ,3,4-oxadiazole.

14. Combating unwanted vegetation by applying post-emergently to thelocus of the vegetation an effective amount of2-diethylamino-5-phenyl-l,3,4-oxadiazole.

l5. Combating unwanted vegetation by applying post-emergently to thelocus of the vegetation an effective amount of2-(3'-nitrophenyl)-5-mercapto-1,3,4- oxadiazole.

" T6. Combating unwanted vegetation by applying post-emergently to thelocus of the vegetation an effecamount of 2-dimethylamino-5-( 2 ',4dimethylphenyl)-l,3,4-oxadiazole.

l7. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2- diethylamino-S -o-tolyl-l ,3,4-oxadiazole hydrochloride. l8. Combating unwanted vegetation byapplying to the locus of the vegetation an effective amount of 2-diethylamino-S-o-tolyl-l ,3 ,4-oxadiazole.

19. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2-(2' -chlorophenyl)-5-dimethylamino-l,3 ,4-oxadiazole.

20. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2- (3 ',4 '-dichlorophenyl l ,3,4-oxadiazole.

21. Combating unwanted vegetation by applying to the locus of thevegetation an efiective amount of 2-(4 -chlorophenyl)-5-diethylamino-1,3 ,4-oxadiazole.

' 22. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2-(4 -chlorophenyl)-5-diethylamin0-1,3,4-oxadiazole hydrochloride.

23. Combating unwanted vegetation by applying to the locus of thevegetation an effective amount of 2-( 3 -chloro-p-tolyl)-5-methyl-1,3,4-oxadiazole.

2. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''-chlorophenyl)-1,3,4-oxadiazole.
 3. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''-bromophenyl)-1,3,4-oxadiazole.
 4. Combating uNwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''-chlorophenyl)-5-methyl-1,3,4-oxadiazole.
 5. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''-chlorophenyl)-5-propyl-1,3,4-oxadiazole.
 6. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''-bromophenyl)-5-methyl-1,3,4-oxadiazole.
 7. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3'',4''-dichlorophenyl)-5-methyl-1,3,4-oxadiazole.
 8. Combating crabgrass by applying pre-emergently to the locus of crabgrass seed an effective amount of 2-(3'',4''-dichlorophenyl)-5-ethyl-1,3,4-oxadiazole.
 9. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(3''4''-dichlorophenyl)-5-propyl-1,3,4-oxadiazole.
 10. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-diethylamino-5-p-tolyl-1, 3,4-oxadiazole.
 11. Combating unwanted vegetation by applying pre-emergently to the locus of the vegetation an effective amount of 2-(m-tolyl)-5-methyl-1,3,4-oxadiazole.
 12. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-diethylamino-5-(4''-fluorophenyl)-1,3,4-oxadiazole.
 13. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-dimethylamino-5-o-tolyl-1,3,4-oxadiazole.
 14. Combating unwanted vegetation by applying post-emergently to the locus of the vegetation an effective amount of 2-diethylamino-5-phenyl-1,3,4-oxadiazole.
 15. Combating unwanted vegetation by applying post-emergently to the locus of the vegetation an effective amount of 2-(3''-nitrophenyl)-5-mercapto-1,3,4-oxadiazole.
 16. Combating unwanted vegetation by applying post-emergently to the locus of the vegetation an effective amount of 2-dimethylamino-5-(2'',4''-dimethylphenyl)-1,3,4-oxadiazole.
 17. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-diethylamino-5-o-tolyl-1, 3,4-oxadiazole hydrochloride.
 18. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-diethylamino-5-o-tolyl-1, 3,4-oxadiazole.
 19. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-(2''-chlorophenyl)-5-dimethylamino-1,3,4-oxadiazole.
 20. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-(3'',4''-dichlorophenyl)-1, 3,4-oxadiazole.
 21. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-(4''-chlorophenyl)-5-diethylamino-1,3,4-oxadiazole.
 22. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-(4''-chlorophenyl)-5-diethylamino-1,3,4-oxadiazole hydrochloride.
 23. Combating unwanted vegetation by applying to the locus of the vegetation an effective amount of 2-(3''-chloro-p-tolyl)-5-methyl-1,3,4-oxadiazole. 